For nearly two decades, immunoassay procedures have provided sensitive diagnostic tools for the in vitro detection of a variety of antigens associated with disease or other physical conditions of clinical significance. Originally such heterogeneous assays used a polyclonal antibody preparation bound to the solid phase. In these assays, a solution of labeled antigen is allowed to compete with antigen in the sample being analyzed for the solid phase antibody. The extent to which the labeled antigen is bound to the solid phase or is detected in the liquid phase can be used as a measure of the presence and quantity of antigen in the sample being analyzed.
Subsequently, non-competitive immunometric assays became available. In these assays, a polyclonal antibody preparation bound to a solid phase was also used. The sample containing the suspected antigen was allowed to contact the solid phase in order for the antigen to bind to the antibodies on the solid phase. Typically, after an incubation step the sample was separated from the solid phase which was then washed and incubated with a solution of additional polyclonal antibodies which had been labeled, for example with a radionuclide, an enzyme, or a fluorescent moiety.
After this second incubation, the unbound labeled antibody was separated from the solid phase and the amount of labeled antibody in either the liquid phase or bound to the solid phase in an antibody:antigen:antibody sandwich was determined as a measure of the presence and/or concentration of antigen in the sample tested.
More recently, immunoassay procedures have been modified to use monoclonal antibodies. For example, U.S. Pat. No. 4,376,110 describes two-site immunometric assays using pairs of monoclonal antibodies, one bound to a solid phase and the other labeled to permit detection. The use of monoclonal antibody pairs which recognize different epitopic sites on an antigen has made it possible to conduct simultaneous immunometric assays in which the antigen and labeled antibody incubations do not require the intermediate washing steps of prior processes.
In the foregoing processes, the solid phase antibody is typically bound to a bead or small particles or coated on a surface. All of these processes characteristically require an incubation period with both the solid phase and labeled antibodies and, as a result, are time consuming even if conducted simultaneously. In fact, it is not unusual for an assay procedure to require several hours to complete. Furthermore, the need to adhere to timed incubation steps and plural washings with measured reagents has largely limited these procedures to large hospital and reference clinical laboratories where highly trained personnel and sophisticated equipment are available to perform the assays. As a result, there has gone unmet a need for a simple and rapid procedure for conducting immunoassays which employ a relatively simple apparatus to make such assays available for use in the physician's office and even for over-the-counter sale to laypersons for use in home health care programs.